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Lift hysteresis at stall as an unsteady boundary-layer phenomenonAnalysis of rotating stall of compressor blade rows requires specification of a dynamic lift curve for the airfoil section at or near stall, presumably including the effect of lift hysteresis. Consideration of the magnus lift of a rotating cylinder suggests performing an unsteady boundary-layer calculation to find the movement of the separation points of an airfoil fixed in a stream of variable incidence. The consideration of the shedding of vorticity into the wake should yield an estimate of lift increment proportional to time rate of change of angle of attack. This increment is the amplitude of the hysteresis loop. An approximate analysis is carried out according to the foregoing ideas for a 6:1 elliptic airfoil at the angle of attack for maximum lift. The assumptions of small perturbations from maximum lift are made, permitting neglect of distributed vorticity in the wake. The calculated hysteresis loop is counterclockwise. Finally, a discussion of the forms of hysteresis loops is presented; and, for small reduced frequency of oscillation, it is concluded that the concept of a viscous "time lag" is appropriate only for harmonic variations of angle of attack with time at mean conditions other than maximum lift.
Document ID
19930092287
Acquisition Source
Legacy CDMS
Document Type
Other
Authors
Moore, Franklin K
Date Acquired
September 6, 2013
Publication Date
January 1, 1956
Report/Patent Number
NACA-TR-1291
Accession Number
93R21577
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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